Fault current limiters (FCL) with the cores saturated by superconducting coils

Abstract

A current limiting device (30, 40, 50, 60) comprising for each phase of an AC supply a closed magnetic core (31) of reduced volume and mass having first and second pairs of opposing limbs (32a, 32b; 33a, 33b), and at least one AC coil (35a, 35b) enclosing opposing limbs (33a, 33b) of the magnetic core (31) and adapted for series connection with a load. A superconducting DC bias coil (34) encloses a limb) (32a, 32b) of the magnetic core (31) for saturating each of the opposing limbs (33a, 33b) in opposite directions by the bias coil (34). Under fault conditions, the AC flux in at least one limb counteracts the DC bias flux, bringing the limb out of saturation. Preferably, current is reduced in the DC bias coils thus bringing both opposing limbs of the core out of saturation.

Description

FIELD OF THE INVENTION[0001]This invention relates to superconducting current limiting devices for AC electric grid.REFERENCES[0002]In the following description, reference will be made to the following publications:[0003][1] B. P. Raju, K. C. Parton, T. C. Bartram, “A current limiting device using super-conducting d.c. bias: applications and prospects,”IEEE Transactions On Power Apparatus &Systems, vol. 101, pp. 3173-3177, 1982.[0004][2] J. X. Jin, S. X. Dou., C. Grantham, and D. Sutanto “Operating principle of a high T-c superconducting saturable magnetic core fault current limiter”. Physica C, 282, Part 4: p. 2643-2644, 1997.[0005][3] J. X. Jin, S. X. Dou., C. Cook, C. Grantham, M. Apperley, and T. Beals, “Magnetic saturable reactor type HTS fault current limiter for electrical application”. Physica C, 2000. 341-348: p. 2629-2630.[0006][4] V. Keilin, I. Kovalev, S. Kruglov, V. Stepanov, I. Shugaev, V. Shcherbakov, I. Akimov, D. Rakov, and A. Shikov, “Model of HTS three-phase satur...

AI Technical Summary

Benefits of technology

[0022]It is therefore an object of the present invention to provide an improved design of FCL with saturated core that includes at least one superconducting DC bias coil placed on a single closed ferromagnetic core, which selves as open core for a single AC coil. Such design of a current limiter allows building the FCL with saturated core having a small mass and dimensions and also reduces or eliminates the transformer coupling between the AC coil and the superconducting DC bias coil(s) thus decreasing AC voltage on the super-conducting DC bias coil(s).

Problems solved by technology

As a result the impedance of the current limiter builds up and limits the current increase.

Also, in known FCLs of this type the impedance of the AC coils does not reach its maximum possible value because the bias coils produce magnetic flux in the cores that reduces the impedance of the AC coils.

This feature is necessary at normal conditions but has a negative effect at fault conditions.

Furthermore, at fault conditions the alternating magnetic field of the AC coils affects the superconducting bias coil, decreasing its critical current.

Second, an additional feedback coil is used to compensate the magnetic flux of the bias coil at the fault regime thus increasing the impedance of the FCL limiting the fault current.

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